• Efficient Mail Submission & Delivery (EMSD) Organization: http://www.emsd.org
  a home for Internet RFC-2524: Efficient Mail Submission & Delivery (EMSD) Protocol. The EMSD Organization is primarily focused on development, maintenance and enhancement of protocols and related technology which address the efficiency requirements of Internet Mail Submission and Delivery. It is the bsis for creation of the open mobile messaging industry.

• Efficient Short Remote Operations (ESRO) Organization: http://www.esro.org
  a home for Internet RFC-2188: Efficient Short Remote Operations (ESRO) Protocol. The ESRO Organization is primarily focused on development, maintenance and enhancement of protocols and related technology which address the efficiency requirements of generic internet applications.

• Fetchmail: http://www.tuxedo.org/esr/fetchmail
  is a full-featured, robust, well-documented remote-mail retrieval and forwarding utility intended to be used over on-demand TCP/IP links (such as SLIP or PPP connections).

• Procmail: http://www.procmail.org
  can be used to create mail-servers, mailing lists, sort incoming messages into separate folder/files, etc.